An amplifier is a device with which a voltage or power of an input signal can be amplified. Among various types of amplifiers, Class AB amplifiers are advantageous in high efficiency, relatively low distortion, relatively low energy consumption of power amplifier transistors and good heat dissipation. At present, such amplifiers are widely used.
FIG. 1 is a schematic diagram of an output stage circuit of a conventional Class AB amplifier. As shown in FIG. 1, when the voltage of the power supply VCC is increased, due to a channel-length modulation effect, the quiescent current flowing through an output circuit, i.e. MP1 and MN1, of the output stage circuit will be increased. As such, the power supply rejection ratio (PSRR) of the output circuit will be decreased and the power consumption of the device will be increased.